Water recirculation in fuel cell power plant

Abstract

A water pump ( 4 ) recirculates water from a water tank ( 3 ) in a heat exchanger ( 2 ) and a fuel cell stack ( 1 ) of a fuel cell power plant via a recirculation passage ( 5 ) A water temperature sensor ( 13 ) detects a water temperature in the recirculation passage ( 5 ). When the water temperature is lower than a predetermined temperature, a controller ( 16 ) recirculates water to the water recirculation passage ( 5 ) by operating a water pump ( 4 ) in order to prevent freezing of water. It is preferred that a heater ( 15 ) is provided to heat the water recirculating in the recirculation passage ( 5 ).

1. A water recirculation device for a fuel cell power plant, the power plant being provided with a fuel cell stack and a heat exchanger, comprising:
 a water tank; 
 a recirculation passage connecting the fuel cell stack, the heat exchanger and the water tank, the recirculation passage comprising a water inlet and a water outlet respectively connected to the fuel cell stack in order to recirculate water in the fuel cell stack; 
 a water pump recirculating water in the recirculation passage; 
 a heater which heats water in the water tank; 
 a water temperature sensor detecting a water temperature of the recirculation passage; 
 a differential pressure sensor which detects a differential pressure of water between the water inlet and the water outlet; and 
 a programmable controller programmed to:
 recirculate water in the recirculation passage by operating the water pump when the water temperature is less than a first predetermined temperature; and 
 activate the heater when the water temperature is less than a second predetermined temperature which is lower than the first predetermined temperature and the differential pressure is larger than a predetermined value. 
 
 
   
   
     2. The water recirculation device as defined in  claim 1 , wherein the water recirculation device further comprises a valve which can prevent water in the recirculation passage from recirculating in the heat exchanger and a temperature sensor which detects a temperature of the heat exchanger, and the controller is further programmed to operate the valve to prevent water in the recirculation passage from recirculating in the heat exchanger when the temperature of the heat exchanger is not greater than a predetermined water temperature. 
   
   
     3. The water recirculation device as defined in  claim 1 , wherein the water recirculation device further comprises a valve which can prevent water in the recirculation passage from recirculating in the fuel cell stack, and a temperature sensor which detects a temperature of the fuel cell stack, and the controller is further programmed to operate the valve to prevent water in the water recirculation passage from recirculating in the fuel cell stack when the temperature of the fuel cell stack is not greater than a predetermined water temperature. 
   
   
     4. The water recirculation device as defined in  claim 1 , wherein the water recirculation device further comprises a valve which discharges water in the heat exchanger in association with an operation of the water pump by introducing air into the heat exchanger through the recirculation passage. 
   
   
     5. The water recirculation device as defined in  claim 1 , wherein the water recirculation device further comprises a valve which discharges water in the fuel cell stack in association with an operation of the water pump by introducing air into the fuel cell stack through the water recirculation passage. 
   
   
     6. The water recirculation device as defined in  claim 1 , wherein the water pump comprises a suction port and a discharge port opening into the water tank, the water pump selectively applying a first operating mode in which the water pump suctions water from the suction port and discharges water into the discharge port and a second operating mode in which the water pump suctions water from the discharge port and discharges water into the suction port, the recirculation passage is configured to recirculate water using a suction force generated at the suction port in the first operating mode, and to fill the fuel cell stack and the heat exchanger with water discharged into the suction port in the second operating mode. 
   
   
     7. A water recirculation device for a fuel cell power plant, the power plant being provided with a fuel cell stack and a heat exchanger, comprising:
 a water tank; 
 a recirculation passage connecting the fuel cell stack, the heat exchanger and the water tank, the recirculation passage comprising a water inlet and a water outlet respectively connected to the fuel cell stack in order to recirculate water in the fuel cell stack; 
 a water pump recirculating water in the recirculation passage; 
 a heater which heats water in the water tank; 
 means for detecting a water temperature of the recirculation passage; 
 means for detecting a differential pressure of water between the water inlet and the water outlet; 
 means for recirculating water in the recirculation passage by operating the water pump when the water temperature is less than a first predetermined temperature; and 
 means for activating the heater when the water temperature is less than a second predetermined temperature which is lower than the first predetermined temperature and the differential pressure is larger than a predetermined value. 
 
   
   
     8. A control method for water recirculation in a fuel cell power plant, the power plant being provided with a fuel cell stack, a heat exchanger, a water tank, a recirculation passage connecting the fuel cell stack, the heat exchanger and the water tank, the recirculation passage comprising a water inlet and a water outlet respectively connected to the fuel cell stack in order to recirculate water in the fuel cell stack, a water pump recirculating water in the recirculation passage, and a heater which heats water in the water tank, the method comprising:
 detecting a water temperature of the recirculation passage; 
 detecting a differential pressure of water between the water inlet and the water outlet: 
 recirculating water in the recirculation passage by operating the water pump when the water temperature is less than a first predetermined temperature; and 
 activating the heater when the water temperature is less than a second predetermined temperature which is lower than the first predetermined temperature and the differential pressure is larger than a predetermined value.